One major focus of immunoparasitology is to isolate parasite antigens which can be used for immunization, and over the last decade, a variety of experimental parasite vaccines have been developed. In many cases, however, these vaccines have only provided partial protection against infection. One reason for the lack of complete protection with some of these vaccines has been our poor understanding of the requirements for successfully presenting candidate immunogens for stimulation of the appropriate immune responses. The long term objective of this application is to use experimental vaccine models to investigate the regulation of T cell subsets, and use this information to design methods to best present potentially protective antigens to the immune system. Cutaneous leishmaniasis, a chronic disease caused by protozoans belonging to the Genus Leishmania, is an excellent model with which to perform these studies. A large body of literature on immunologic mechanisms controlling this infection exists which provides a foundation for these studies. In addition, the disease is of significant public health importance and research efforts are currently focused on vaccine development. The Specific Aims of this proposal include: 1) Identification, isolation and characterization of leishmanial antigens recognize by T cells. The approach is to develop protective T cell clones and identify the antigen recognized by these clones by T cell immunoblotting. Defined antigens will be isolated by either (a) sequencing; (b) production of monoclonal antibodies and screening a cDNA library; or (c) direct screening of a cDNA library with the T cell clones. Once isolated these antigens will be tested for their ability to provide protection against Leishmania major infection in BALB/c mice. Further studies will characterize the immunologic and immunochemical characteristics of protective antigens. 2) Identification of mechanisms regulating T cell subsets in vaccine induced immunity. These studies will be directed at identifying how CD4+ T cell subsets, TH1 and TH2, are regulated, and what role the immunizing antigen plays in their development following vaccine induced immunity. Experiments will include cloning of T cells from protected and non-protected animals and analysis of their antigen specificity and pattern of lymphokine production. Studies will include depletion of particular T cell subsets, or lymphokines, to determine their influence on immunity. Based upon the above results, experiments will be designed to enhance methods of antigen presentation for induction of protective immunologic responses. These studies will in large part concentrate on the role of IFN-gamma as an in vivo regulator of T cell activation. Finally, the ability to abrogate lesion development after infection by altering the balance of T cell subsets will be investigated.